The field of this invention is apparatus and methods for actuation or movement of a load member by two or more synchronized hydraulic motors. More particularly, this invention relates to apparatus and methods for moving a control portion of an aircraft via hydraulic motors. Specifically, this invention relates to apparatus and methods for moving thrust reverser structure associated with an aircraft jet propulsion engine between deployed and stowed positions via multiple synchronized motors of the extensible type wherein such motors are hydraulically powered. Synchronization of such hydraulic motors is maintained during their operation despite load variations therebetween. The force which the motors may exert upon the thrust reverser structure may be limited to a predetermined value.
A number of conventional actuation systems having multiple synchronized hydraulic motors are known. These conventional systems may be conveniently classified into three groups, as follows: First, systems having a servo valve or valves feed back coupled with the load member and controlling the flow of hydraulic pressure fluid to the motors. Second, systems employing a flow distributor to apportion hydraulic pressure fluid flow among the motors. Third, systems having cross-connected or cascade-connected working or synchronization volumes in the various motors so that movement of one motor causes corresponding movement of the cross-connected motor. Of course, some conventional systems are hybrids of the above three groups. For example, a flow distributor may take the form of a flow sensor controlling a servo valve or valves. Further, a cross-connected system may include a servo valve controlling the flow of pressure fluid to the working volumes of the motors. Regardless of the particular form taken by conventional systems for synchronizing hydraulic motors, these conventional systems suffer from many deficiencies. Among these deficiencies are undue complexity, a failure to precisely synchronize the motors, difficulty in purging air from the system, and the concentration of applied force in one motor should a jam of the load member occur.
U.S. Pat. Nos. 3,476,016; 2,759,330; 2,286,798 and 3,855,794 illustrate conventional synchronized hydraulic motor systems.
In view of the recognized deficiencies of conventional hydraulic actuation systems, such hydraulic actuation has heretofore been considered inappropriate for use in moving aircraft control structures such as thrust reverser structure. Consequently, the most common device employed for deploying and stowing aircraft thrust reversers are ball screw units. Each thrust reverser conventionally is moved by two or more ball screw units which are synchronized by gears and shafting which cross couples the ball screws. The screws can be individually driven by hydraulic motors, or the entire group can be driven by one motor.
Such ball screw type of actuators also have many recognized deficiencies including unevenly distributed force output, undue complexity, and sudden failure of shafting or gearing thereof so that the system becomes inoperable.